Lighting device for a motor vehicle, incorporating means for protection against electrostatic discharges

ABSTRACT

The invention proposes a lighting device for a motor vehicle. Such a device includes one or more electronic circuits incorporating electronic components sensitive to an electrostatic discharge. Thanks to the features of the invention, the components are protected by encouraging the controlled flow to ground of any electrostatic discharges. All portions of one or more electronic circuits can therefore be protected by preventing random electrostatic discharges liable to destroy or to degrade sensitive electronic components.

The invention relates to the field of lighting devices for a motorvehicle. The invention concerns in particular such devices usingelectronic components sensitive to electrostatic discharges, such aslight-emitting diodes, for example.

In the field of lighting devices for motor vehicles, the use of lightsources such as light-emitting diodes (LED), organic light-emittingdiodes (OLED) or laser diodes is increasingly specified. The placementof these lighting means along precise contours in actual fact makes itpossible to create interesting and individual optical signatures.However, these are sensitive electronic components, notably sensitive toelectrostatic discharges. During the service life of a motor vehicle,such components may be exposed to electrostatic discharges inside theheadlight of which they form part. For example, because of friction ofthe external air on the outer lenses of a headlight, portions of thelatter may come to carry static charges. If the light sources aresubjected to discharges coming from these portions, there is a high riskof premature deterioration or even premature destruction of theelectronic components.

In order to protect light sources, it is known to provide protectionelectronic circuits in the lighting device. For example, an electricalcapacitor may be connected in parallel with an LED, the capacitor beingable to absorb any surge. However, the cost of such a solution increasesin proportion to the number of LEDs used. Moreover, such protectioncircuits occupy a large portion of the respective printed circuitboards, and the amount of room inside the device is limited.

The patent document US 2002/0151200 A1 describes a circuit element forprotecting an electronic device from surges that occur within theelectronic circuit including a sensitive component. Such a system can beuseful only if the surge can occur only at a predefined location of thecircuit to be protected. Means adapted to redirect the surge to groundon the upstream side of the sensitive component may then be incorporatedin the circuit to the protected. Such a solution is not applicable tocases as described, however, in which an electrostatic discharge mayoccur at random to an electronic circuit including one or more sensitivecomponents. As the discharge can occur in different portions of thecircuit to be protected, this known solution is not able to solve theproblem described.

An objective of the invention is to alleviate at least one of theproblems raised by the prior art. To be more precise, an objective ofthe invention is to propose a lighting device incorporating protectionof electronic components sensitive to an electrostatic discharge.

The invention consists in a lighting device for a motor vehicle. Thedevice includes a substrate on which is arranged at least one element ofan electronic circuit. The electronic circuit includes at least oneelectronic component sensitive to an electrostatic discharge. The devicealso includes a structure that is distinct from the substrate and liableto carry electrical charges. The shortest distance between the structureand each of the elements of the circuit is equal to D1. The devicefurthermore comprises an electrically conductive means connectedelectrically to ground, that is to say to the zero reference potential.The device is noteworthy in that it comprises at least one protectiveelement protecting against electrostatic discharges which is disposed onsaid structure and linked electrically to the latter, the smallestdistance between the protective element and the electrically conductivemeans, D2, being less than D1.

Preferably, the protective element can be arranged so that the distancebetween the protective element and the sensitive electronic component isgreater than the distance between the protective element and theelectrically conductive element connected to ground, so that there is noflow of charge from the protective element to the component to beprotected.

Preferably, the protective element is situated on a surface of saidstructure, said structure being oriented towards said substrate.

The distance D2 may preferably be strictly less than 10 mm, whereas thedistance D1 may be strictly greater than 10 mm.

Preferably, the distance D2 is non-zero and there is no physical contactbetween the protective element and the electrically conductive meansconnected to ground.

The elements of the electronic circuit may preferably includeelectrically conductive tracks and electronic components connected tothe tracks.

The protective element may preferably be a plastic material element, atleast one portion of its surface being coated with an electricallyconductive layer. This may be a layer of copper, aluminum or a metalalloy including an electrically conductive metal, for example.

The protective element may preferably have a base and extend from thisbase situated at the level of said structure, tapering so as to form atip directed towards said electrically conductive means connected toground.

The electrically conductive means may preferably comprise a zone of thesubstrate.

Preferably, the device can comprise a distinct metallic portion separatefrom the substrate, for example a heat dissipation means such as aradiator, of which said electrically conductive means forms part.

The electrically conductive means can be a zone of the surface of thesubstrate or of said metallic portion.

The protective element may preferably comprise an electricallyconductive metallic material.

Preferably, the protective element may be integral with said structure.The protective element may preferentially be produced by deformation, inparticular local, of the structure, for example at a location situatedsquare with the electrically conductive means connected to ground.

The protective element may preferably be a portion which is fastened tosaid structure. The portion may preferably be fixed to the structure byscrewing or by gluing.

The protective element may preferably be produced or fixed on a zonedevoid of optical and/or esthetic role of said structure.

The substrate may preferably be the substrate of a printed circuit board(PCB). The substrate may preferably be plane.

Alternatively, the substrate may be the substrate of an interconnectiondevice (MID) having a complex geometry. The substrate of theinterconnection device may be molded or machined.

The electronic component may preferably be a light-emitting diode (LED),a laser diode or an organic light-emitting diode (OLED). The electroniccircuit may preferably include a plurality of LEDs, OLEDs or laserdiodes sensitive to electrostatic discharges.

The electrical circuit may include a group including a plurality ofelectronic components sensitive to electrostatic discharges, theelectronic components of this group being interconnected. In this case,the device may include a protective element associated with this groupand that is adapted to protect all the electronic components of thisgroup on its own.

The electrical circuit may preferably include a plurality of groups eachincluding a plurality of electronic components sensitive toelectrostatic discharges, the electronic components of each group beinginterconnected. In this case, the device may include a plurality ofprotective elements, each protective element being associated on aone-to-one basis with one of the groups and being adapted to protect allthe electronic components of that group on its own.

The structure liable to carry electrical charges may preferably be anelement of the outer lens of the lighting device. It may in particularbe a metalized plastic portion liable to carry electrical charges. Theportion may preferably be aluminized.

The device may preferably be a head light or a rear light of a motorvehicle.

Compared to known solutions, the “lightning arrestor” effect produced bythe features of the present invention makes it possible to reduce themanufacturing costs of a lighting device for a motor vehicle whilstproviding long-lasting protection of the electronic components sensitiveto electrostatic discharges. The measures in accordance with theinvention define a low-impedance path between the structure liable to becharged, by way of the protective element connected thereto, and a zoneelectrically connected to ground, thereby encouraging the creation ofdischarge paths between the protective element on the one hand and thezone connected to ground on the other hand. In actual fact, as thedistance D2 defined in accordance with the invention is less than thedistance D1, the device encourages an electrostatic discharge betweenthe protective element electrically connected to the structure liable tocarry electrical charges, and the zone connected to ground, relative tothe elements of the electronic circuit. The longevity of the electroniccomponents and of the device are therefore increased and at the sametime the complexity of the electronic circuits involved is reducedcompared to known solutions. In actual fact, by applying the proposedinvention, it is possible to dispense with dedicated protection circuitsinvolving a capacitor for each of the light sources of such a device.This is of particular interest when a large number of such lightsources, for example LEDs, is used in a lighting device in order toobtain a particular optical signature. One or more protection elements,easy to produce, and positioned in accordance with the features of theinvention are capable of protecting a plurality of such light sourcesagainst random electrostatic discharges stemming for example fromcharges accumulated on a face of an outer lens of the device.

Other features and advantages of the present invention will be betterunderstood with the aid of the description of an example and thedrawings, in which:

FIG. 1 shows diagrammatically a lateral section of a preferredembodiment of the device in accordance with the invention;

FIG. 2 shows diagrammatically a lateral section of a preferredembodiment of the device in accordance with the invention;

FIG. 3 shows diagrammatically a lateral section of a preferredembodiment of the device in accordance with the invention.

In the following description, similar reference numbers will be used todescribe similar concepts across different embodiments of the invention.Thus, the numbers 100, 200, 300 denote a device in accordance with theinvention in three different embodiments.

Unless specifically indicated otherwise, the technical featuresdescribed in detail for a given embodiment may be combined with thetechnical features described in the context of other embodimentsdescribed by way of nonlimiting example.

In the following description, components necessary for a lighting devicefor a motor vehicle to operate, but which have no direct impact on thepresent invention, will not be described explicitly, in order topreserve the clarity of the disclosure of the invention. In knownmanner, the light sources of a lighting device for a motor vehicle aresupplied with power by a current source internal to the vehicle, such asthe battery of the vehicle, and via a power supply control devicegenerally including at least one converter. Suitable converters areknown in themselves in the art and are able to convert an input directcurrent voltage into a different output direct current voltage suitablefor the supply of power of the light source or sources of the device. Alighting device may also include in known manner optical means intendedto guide the light rays emitted by the light source of sources of thedevice. These may be optical lenses and/or waveguides, for example. Adevice in accordance with the invention may further provide one or morelighting functions of the motor vehicle in which it is installed. Thesemay be, by way of nonlimiting example, daytime running lamp, high-beamor turn indicator functions.

FIG. 1 shows a diagrammatic illustration of the elements of a device 100in accordance with a preferred embodiment of the invention. The deviceincludes a substrate 110 that supports an electronic circuit 120. It mayfor example be a generally plane printed circuit board (PCB) or othersubstrates known in themselves in the art. The electronic circuit 120includes conductive tracks 122 and components 124 connected by theconductive track. By way of nonlimiting example, a light-emitting diode(LED) 124 is shown. Although the substrate shown supports only onecircuit, it may generally include a plurality of separate circuitsproviding different functions. The formation of conductive tracks on asubstrate and the fixing of the components to the substrate are known inthemselves in the art and will not be described in detail in the contextof the present invention.

The device also includes a structure 130 that is liable to carry, atleast temporarily, electrical charges. It is for example an element ofthe outer lens of the lighting device, which may become electricallycharged when the vehicle is driven because of friction with the externalair. It may also be an embellishment of the device. In the FIG. 1illustration, the structure 130 is shown as being plane. The structuremay nevertheless have different and more complex geometries. Forexample, the structure may have a geometry that is curved in at leastone direction. The shortest distance between the substrate that supportsthe circuit 120 and the structure is indicated by the measurement D1.The distance in question is considered between all the points of thesurface of the structure and all the points of the circuit to beprotected.

In order to prevent a charge present on the structure 130 beingdischarged to one of the elements 122, 124 of the electronic circuit120, which would cause damage to the components 124, a protectiveelement or protection element 140 and an electrically conductive means150 are provided. The protection element 140 has the single function ofprotecting the electronic circuit 120 against electrostatic discharges.

The protective element 140 may be integral with the structure 130 whichis preferably made of plastic and of which at least the surface directedtowards the substrate 110 is aluminized or metalized. The protectiveelement 140 may in particular be the result of a local deformation ofthe structure 130. The protective element is disposed so as not toimpair optical or esthetic functions of the structure 130. In the caseillustrated, it is a separate portion linked in an electricallyconducting manner to the structure 130, in such a way that staticelectrical charges accumulated on the structure 130 can migrate towardsthe protective element 140. Fixing is carried out by gluing, by screwingor by other suitable means.

The protective element extends from the surface of the structure 130which is directed towards the substrate 110 towards an electricallyconductive element 150, which is connected to ground. The disposition ofthe protective element 140 and of this element 150 connected to groundis such that the distance D2 which separates them is non-zero andstrictly less than the distance D1. For example, the distance D2 isstrictly less than 10 mm whereas the distance D1 is strictly greaterthan 10 mm.

These dimensions are obviously not limiting on the features of theinvention. An electrical charge on the structure 130 seeks theevacuation path with the lowest impedance. Using the features of theinvention, this path includes the protection element 140 and the zone150 that is electrically connected to the zero potential or ground. Theelectrical charge on the structure is therefore discharged via anelectrical arc between the structure 130, by means of the protectionelement 140, and the zone 150, from which it is evacuated to ground.Such a discharge is therefore diverted from the circuit 120 withoutpassing through the components 124 or the conductive tracks 122. Thecircuit 120 is therefore protected without adding additional electroniccomponents to the circuit.

The invention applies in an analogous manner to more complex geometries,both at the level of the structure potentially carrying charges and atthe level of the substrate supporting the electronic circuit to beprotected. One example is illustrated by the FIG. 2 section, in whichthe circuit 220 including conductive tracks and an LED 224 is part of asubstrate 210 of MID (“molded interconnect device”) type or of molded ormachined interconnection device type. The production of such devices isknown in itself in the art and notably makes it possible to produceelectronic circuits on substrates that have a complex geometry. Thedevice 200 shown includes thermal dissipation means 250 such as a metalheatsink. The thermal dissipation means are connected to ground and areadapted to dissipate the heat produced by the components of theelectronic circuit 220. In the example shown, the protection element 240is fixed to the charge-carrying structure 230 and extends in thedirection of a surface zone 250 of the metallic radiator 260 which isconnected to ground. Alternatively, it is also possible to envisage aplastic element whose surface is at least partially metalized, themetallic coating being connected to ground, so as to implement theconductive element 250. Electrical charges accumulated on the structure230 are therefore evacuated to ground by traveling through theprotection element 240 and the conductive element 250.

The embodiment illustrated by the FIG. 3 diagram is similar to thearrangement shown in FIG. 1. Nonetheless, the protection element 340 isintegral with the structure 330. The protection element has a spigotshape having a broad base and tapers with increasing distance from thestructure 330, so as to form a tip directed towards the conducting zone350 connected to ground. The zone 350 is in this embodiment formed by aconductive span on the substrate 310 which carries the electroniccircuit to be protected. The distance D2 between the tip of the element350, which has a concentration of static electrical charges, and thezone 350 is less than the distance D1 such as defined previously, insuch a way that the charges accumulated in the tip flow by formation ofan arc between the point and the zone 350, without passing through thecomponents of the electronic circuit 320.

Although in the embodiments that have just been described by way ofexample a single protective element 130, 230, 330 is shown, a pluralityof similar elements may be disposed in the manner that has just beendescribed. It goes without saying that the protective element orelements is or are adapted to protect any electronic circuit disposed onone or more substrates provided that the distance D2 as defined is lessthan the shortest distance between the structure liable to be chargedand each of the elements of each of the circuits to be protected.

Based on the description that has just been given and the accompanyingfigures, the application of the invention to more complex geometrieswill be obvious to the person skilled in the art having generalbackground knowledge in the field.

The invention claimed is:
 1. Lighting device for a motor vehicle,including a substrate on which is arranged at least one element of anelectronic circuit including at least one electronic component sensitiveto an electrostatic discharge, and a structure that is distinct from thesubstrate and liable to carry electrical charges, the shortest distancebetween the structure and each of the elements of the circuit beingequal to D1, and an electrically conductive means connected electricallyto ground, wherein the device comprises at least one protective elementprotecting against electrostatic discharges which is disposed on thestructure and linked electrically to the latter, the smallest distancebetween the protective element and the electrically conductive means,D2, being less than D1.
 2. Device according to claim 1, wherein theelectrically conductive means comprises a zone of the substrate. 3.Device according to claim 1, wherein the device comprises a distinctmetallic portion separate from the substrate, of which said electricallyconductive means forms part.
 4. Device according to claim 1, wherein theprotective element comprises an electrically conductive metallicmaterial.
 5. Device according to claim 1, wherein the protective elementis integral with said structure.
 6. Device according to claim 1, whereinthe protective element is a portion which is fastened to said structure.7. Device according to claim 1, wherein the protective element extendsfrom said structure to the electrically conductive means.
 8. Deviceaccording to claim 1, wherein the substrate is the substrate of aprinted circuit board (PCB).
 9. Device according to claim 1, wherein thesubstrate is the substrate of an interconnection device (MID) having acomplex geometry.
 10. Device according to claim 1, wherein theelectronic component is a light-emitting diode (LED), a laser diode oran organic light-emitting diode (OLED).
 11. Device according to claim 1,wherein the structure is an element of the outer lens of the lightingdevice or a metalized plastic portion liable to carry electricalcharges.
 12. Device according to claim 1, wherein the device is a frontlight or a rear light of a motor vehicle.
 13. Device according to claim2, wherein the protective element comprises an electrically conductivemetallic material.
 14. Device according to claim 2, wherein theprotective element is integral with said structure.
 15. Device accordingto claim 2, wherein the protective element is a portion which isfastened to said structure.
 16. Device according to claim 2, wherein theprotective element extends from said structure to the electricallyconductive means.
 17. Device according to claim 2, wherein the substrateis the substrate of a printed circuit board (PCB).
 18. Device accordingto claim 2, wherein the substrate is the substrate of an interconnectiondevice (MID) having a complex geometry.
 19. Device according to claim 2,wherein the electronic component is a light-emitting diode (LED), alaser diode or an organic light-emitting diode (OLED).
 20. Deviceaccording to claim 2, wherein the structure is an element of the outerlens of the lighting device or a metalized plastic portion liable tocarry electrical charges.